An oxidation model for carbon surfaces is developed where the gas-surface reaction mechanisms and corresponding rate parameters are based solely on observations from recent molecular beam experiments. In the experiments, a high energy beam of oxygen (93% atoms and 7% molecules) was directed at a high-temperature carbon surface. The measurements revealed that CO was the dominant reaction product and that its formation required a high surface coverage of oxygen atoms. As the carbon sample temperature was increased during the experiment, the surface coverage was reduced and the production of CO diminished. Most importantly, the measured time-of-flight distributions of surface reaction products indicated that CO and CO2 were predominately formed through thermal reaction mechanisms and not impulsive reactive scattering. These observations enabled the formulation of a finite-rate oxidation model including surface-coverage dependence, similar to existing finite-rate models used in computational fluid dynamics (CFD) simulations. However, each reaction mechanism and all rate parameters of the new model are determined individually based on the molecular beam data. The new model is compared to existing models using both zero-dimensional gas-surface simulations and full CFD simulations of hypersonic flow over an ablating surface. The new model predicts similar overall mass loss rates compared to existing models, however, the individual species production rates are completely different. The most notable difference is that the new model (based on molecular beam data) predicts CO as the oxidation reaction product with virtually no CO2 production, whereas existing models predict the exact opposite trend.
|Original language||English (US)|
|Title of host publication||46th AIAA Thermophysics Conference|
|Publisher||American Institute of Aeronautics and Astronautics Inc, AIAA|
|State||Published - 2016|
|Event||46th AIAA Thermophysics Conference, 2016 - Washington, United States|
Duration: Jun 13 2016 → Jun 17 2016
|Name||46th AIAA Thermophysics Conference|
|Other||46th AIAA Thermophysics Conference, 2016|
|Period||6/13/16 → 6/17/16|
Bibliographical noteFunding Information:
This work was sponsored by the Air Force Office of Scientiffic Research (AFOSR) under MURI grant FA9550-10-1-0563. The views and conclusions contained herein are those of the author and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the AFOSR or the U.S. Government. Savio Poovathingal would like to acknowledge support through Doctoal Dissertation Fellowship (DDF) from University of Minnesota. Vanessa J. Murray is grateful for support awarded by DoD, Air Force Office of Scientiffic Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 (Code of Federal Regulations) CFR 168a.
© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All right reserved.